The overall objective is to determine how cell surface active hormones initiate their biological effects by studying the physical and chemical consequences in the membrane after peptide and catecholamine binding. Our working hypothesis is that the specific hormone receptor units act as transducers of the hormone message to produce conformationa changes at the receptor and other membrane components. Thus our specific objective is to study cell surface hormone binding and its consequences in bulk properties of the membrane as well as ion distribution and specific membrane enzyme activities. We propose to determine the effect of catecholamine hormones on erythrocyte membrane potential and relate this to the effects on membrane phosphorylation and calcium binding in human erythrocytes. In addition, in the isolated adipocyte we shall determine the role of membrane potential in the anti-lipolytic and lipolytic response of insulin and catecholamines. In isolated adrenal chromaffin cells we shall elucidate the role of cell surface ligands, calcium and membrane potential on the regulation of catecholamine secretion.